It is well known in the art to use control moment gyros (CMGs) to control the momentum and adjust the orientation of spacecraft. CMGs and momentum control systems are described, for example, in Patents or Patent Publications: US-2002/0040950 A1 to Staley et al; U.S. Pat. No. 6,231,011 B1 to Chu et al; U.S. Pat. No. 6,154,691 to Bailey; U.S. Pat. No. 6,360,996 B1 to Bockman et al; U.S. Pat. No. 6,128,556 to Bailey; U.S. Pat. No. 6,131,056 to Bailey et al; U.S. Pat. No. 6,285,927 B1 to Rongsheng et al; U.S. Pat. No. 6,305,647 B1 to Defendini et al; U.S. Pat. No. 6,039,290 to Bong Wie et al; and U.S. Pat. No. 6,311,931 B1 to Smay. It is known to use CMG arrays to adjust the momentum of the spacecraft and/or vary its orientation in three dimensions.
A problem with prior art CMG arrays is that when one or more of the CMGs in the array fails, it is often difficult or impossible to continue controlling the spacecraft momentum and/or orientation using the remaining CMGs. Even if some control continues to be possible, the available momentum control space is generally much reduced because the orientation of the remaining CMGs is no longer optimal. (The momentum control space is the range of momentum values that can be achieved at any given time using the available CMG array). A further problem often encountered with spacecraft is that upon construction or arriving in orbit, the mass properties of the spacecraft are not exactly as initially predicted, and the CMG orientation initially set up is less than optimum for the actual mass properties after construction or in arrival orbit. A still further problem is that during the life of the spacecraft due, for example, to the expenditure of maneuvering fuel or other supplies or cargo released or captured, the mass properties of the spacecraft may change with time. Once again, an initial CMG array orientation may no longer provide the maximum momentum control space. Thus, a need continues to exist for a means and method for improving the reliability and capability of spacecraft momentum control with CMG arrays, in particular, being able to compensate in whole or in part for: (1) failure of one or more of the individual CMGs of an array, or (2) different or altered mass properties of the spacecraft after construction or launch, or (3) a combination thereof.
Accordingly, it is desirable to provide a means and method whereby one or more of the active CMGs of a spacecraft can be reoriented to maximize the attainable momentum control space. In addition, it is desirable that the reorientation be able to be performed either prior to launch and/or remotely in-orbit. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.